Microwave oven interlock switch actuator

ABSTRACT

A microwave oven apparatus is disclosed having means for actuating electrical safety interlock switch means upon movement of the oven door member. Positive mechanical linkage means include an arm actuator pivotally joined to a peripheral wall of the door frame. A bushing member is pivotally connected to a peripheral wall of the access opening and provides means to constrain and guide the movememt of the arm actuator. First and second individual pivots are defined and the combination of the constrained movement of the arm actuator and bushing members results in a substantially linear movement upwards and sidewards of the arm to actuate the interlock switch means upon the closing of the oven door.

United States Patent 1 Rosenberry Jan. 28, 1975 1 1 MICROWAVE OVEN INTERLOCK SWITCH [73] Assignee: Amana Refrigeration, lnc., Amana.

Iowa

[22] Filed: Dec. 13, 1973 [21] Appl. No.: 424,584

[52] 11.8. C1. 2l9/10.55 C, ZOO/61.82 [51] Int. Cl. 1-105b 9/06 [58] Field of Search 219/1055; ZOO/61.62, 61.81, 200/61.82

[56] References Cited UNITED STATES PATENTS 868,348 10/1907 Kramer ZOO/61.62 3,748,423 7/1973 Haagensen 219/1055 Primary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm-Edgar O. Rost; Joseph D. Pannone; Harold A. Murphy [57] ABSTRACT A microwave oven apparatus is disclosed having means for actuating electrical safety interlock switch means upon movement of the oven door member. Positive mechanical linkage means include an arm actuator pivotally joined to a peripheral wall of the door frame. A bushing member is pivotally connected to a peripheral wall of the access opening and provides means to constrain and guide the movememt of the arm actuator. First and second individual pivots are defined and the combination of the constrained movement of the arm actuator and bushing members results in a substantially linear movement upwards and sidewards of the arm to actuate the interlock switch means upon the closing of the oven door.

5 Claims, 6 Drawing Figures MICROWAVE OVEN INTERLOCK SWITCH ACTUATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to microwave oven apparatus and mechanical linkage means for actuating electrical interlock switch means.

2. Description of the Prior Art Microwave oven apparatus is widely used in the preparation of numerous products due to the rapid preparation times resulting from the dielectric heating phenomenon. The energy sourcetypically employed for such apparatus is the magnetron oscillator of the type described in the text Microwave Magnetrons, Vol. 6, Radiation Laboratory Series, by G. B. Collins,

McGraw-Hill Book Company, Inc., 1948. The high frequency energyoscillations are radiated within an oven enclosure and the energy is uniformly distributed by such means as mode stirrers to heat a load by molecular friction resulting from the absorbed energy. In the conventional apparatus the oven enclosure is capable of supporting a plurality of free-space wavelengths of the operating frequency. The allocated frequencies for such heating apparatus are assigned by the Federal Communications Commission and are either 915 i 13 MHZ or 2,450 i 50 MHZ in the so-called industrial, scientific and medical band of the electromagnetic energy spectrum. The term microwaves" is intended to define electromagnetic energy radiation having wavelengths in the order of 1 meter to 1 millimeter and'frequencies in excess of 300 MHz.

Certain safety standards have been established by regulatory agencies such as the Department of Health, Education and Welfare, as well as the United States of America Standards Institute, for the control of the amount of energy leakage around the door enclosing an access opening for the oven enclosure. In addition, safety devices, such as electrical interlock switches, are required to be associated with the access oven doors, as well as the electrical controls, for operation of the apparatus to interrupt the application of energy upon the sensing of any fault prescribed by the safety standards. Since the interlock switches are required to open and close each time the apparatus is operated, such devices must be completely reliable and adequately disable the electrical circuits at any time that a hazardous condition arises. Over extended periods of time the mechanical linkage means typically employed in the operation of the interlock safety switches, particularly the door-actuated type, may become subject to damage due to wear or result in damage to energy seal gaskets surrounding the peripheral walls of the access opening and door for the control of the energy leakage.

SUMMARY OF THE INVENTION the bushing member is secured to a peripheral wall of the access opening. The axes of rotation provided by the pivot means results in the arm actuator having a modified linear movement for positive engagement of a spring lever arm which operates the interlock switch means. Typically, such interlock switches are serially connected in the electrical circuits so that should any such switch means fail to operate the entire apparatus would be inoperative. In prior art configurations, spring-biassing means, as well as counterbalancing arms, have been employed in door members to provide for the contact between the actuator means and the interlock switch lever arm. Such arrangements are quite often subject to failure due to breakage or binding.

In an exemplary embodiment of the invention the arm actuator comprises a metallic member, such as a plated steel bar. The arm guide bushing member which supports and constrains the actuator comprises a durable plastic material of a nylon or selcon composition. The pivot support means for the arm actuator and bushing members comprise force-fitted cold-rolled steel pins having an enlarged head and a plating such as zinc. The described mechanical linkage for actuating the interlock switch means has no sharp projections or edges which can rip door energy seal gaskets and is capable of a long life expectancy and dependable performance.

BRIEF DESCRIPTION OF THE DRAWINGS Details of the illustrative embodiment of the invention will be readily understood after consideration of the following description and reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view partially broken away of a portion of an illustrative microwave oven apparatus embodying the invention;

FIG. 2 is a perspective view of an arm actuator of the invention;

FIG. 3 is an end view of an assembled arm guide bushing member of the invention;

FIG. 4 is an exploded perspective view of the components of the arm bushing member assembly shown in FIG. 3;

FIG. 5 is a plan view of a portion of the door member and a portion of the oven apparatus with the top wall removed to disclose the linkage arrangement of the invention with the door in the open position; and

FIG. 6 is a plan view of the illustrative embodiment similar to that shown in FIG. 5 with the door in the closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 a microwave oven apparatus 10 embodying the invention is shown comprising conductive walls 12 defining therebetween an oven enclosure 14. Peripheral walls 16 surround an access opening and-in this embodiment a door member 18 supported by a side hinge arrangement 20 encloses the opening. The door member is of the conventional type provided with a choke energy seal arrangement disposed beneath a cover member 22 of a plastic material, such as Lexan, together with secondary energy absorbing gaskets 24 of rubber impregnated with ferrite or plastic impregnated with carbon, to suppress any escaping energy. The choke arrangement has not been described in detail in this specification in the interest of clarity in understanding the mechanical linkage arrangement of the invention. The energy source comprising a magnetron and associated launching and distribution means have not been illustrated since they are now believed to be well known.

The door member includes a frame 26 having a slot 28 in a peripheral wall for engagement by end of a hand-actuated latch lock member 30 having an associated interlock switch for control of the operation of the oven apparatus. The latch member 30 is positioned within the upper control panel 32 which also supports a timer 34 for the operation of the apparatus. The door member 18 is also provided with a hook member 36 to engage a slot 38 in a peripheral wall 16 of the access opening. Another safety interlock switch is associated with the hook member 36 and has not been detailed for the sake of clear understanding of the structure of the present invention. The cover member 22 is provided with a transparent window 40 for viewing the interior of the oven enclosure.

The exemplary mechanical linkage arrangement 42 for actuating of a door interlock switch is coupled between the door frame peripheral walls 26 and the access opening peripheral walls I6. Details of the assembly linkage will now be described with reference being directed to FIGS. 2-4 inclusive. As shown in FIG. 2, the door arm actuator 44 comprises a substantially flat rigid metallic member of a material such as steel, suitably plated for durability. The actuator is provided with a hook-type stop member 46 to limit the overall excursion of this component. The other end of arm actuator 44 is provided with an opening 48 to facilitate the pivotal mounting of this member to the peripheral door frame wall 26'by a pivot pin 50 and tab 52 arrangement as shown in FIG. 1. The arm actuator 44, therefore, is pivoted about a first axis of rotation determined by the pin 50 which is fixedly secured to the door member 18.

In FIGS. 3 and 4 a guide bushing member assembly 54 is shown which constrains and supports the arm actuator 44. Upper and lower bushing body members 56 and 58, fabricated of any durable plastic material, such as nylon or selcon, are joined together to provide the second pivotal member having aligned pivot pin openings 60 and 62, as well as a slot 64 for slidably engaging the arm actuator 44. The upper bushing body member 56 is further provided with a cored area 66 to lighten the weight of the overall structure. Tab portions 68 and 70 extend from one sidewall of bushing body member 56. The lower companion body member 58 has arched wall openings 72 and 74 for mating with the tabs 68 and 70 and to provide the clearance for slot 64 when the components are joined together. Bushing member assembly 54 is pivotally secured by means of a pivot pin 76 extending through aligned openings 60 and 62 to an access opening peripheral wall 16.

Referring next to FIGS. and 6 the operation of the linkage arrangement intercoupling the door actuator and bushing member means for contacting and closing the interlock switch means will now be described. FIG. 5 represents the door member in the open position while FIG. 6 represents the closed position. A safety interlock switch 78 comprises a lever arm 80 of a substantially S-shaped configuration and a resilient metallic material. The lever arm contacts snap button 82. The internal electrical contacts are normally in the open position so that it is necessary for the lever arm 80 to be depressed in order to close the circuits and operate the microwave oven apparatus. Terminal connectors 84, 86 and 88 connect the interlock switch 78 to the appropriate electrical circuits for operation of the high voltage supply, as well as all associated electrical circuitry for the operation of the apparatus. Details of such circuitry have been purposely omitted in this description for the sake of clarity in an understanding of the invention. The electrical wiring interconnecting the interlock switch terminals to the appropriate circuitry extend through openings 90 and 92.

Referring first to FIG. 5 the door assembly is shown in the open position. The arm actuator 44 is constrained and guided in its movement-by bushing member 54 and the door member can be moved to the limited excursion point determined by the door stop hook 46. The arm actuator 44pivots about the axis determined by the pin 54 secured to the tabs 52 and describes a circular path 94 of a substantially large radius if the actuator member 94 was freely movable. As a result of the constrained movement of this bushing member 54 a much smaller portion of a circular path 96 can be described by the arm actuator 44. The axis of rotation of member 54 about pivot pin 76 is described by circular path 100. The limited movement results in a combined substantially linear movement of the arm actuator in a first direction substantially parallel to the sidewalls of the oven enclosure shown by arrow [06. After a predetermined point is reached the arm actuator 44 moves sideward in an arc, arrow 108, into the engagement position with lever arm 80 of the interlock switch and closes button 82 to actuate all the apparatus. It will be noted that a circular path described about the hinge member 20 axis, as indicated by the partial circular line 98, falls slightly short of intersecting the axis of the pivot pin 50 which assists in the attainment of the overall desired movement of the arm actuator 44.

In FIG. 6 the mechanical linkage arrangement of the invention is shown with the door member in the closed position. It will be noted that the pivot path 100 of the bushing member 54 and the limited circular path 96 of the pivotal arm actuator 44 are juxtapositioned with a spacing between the axes of rotation 50 and 76 of substantially less than the length of the arm actuator 44. In an exemplary embodiment the distance between the two axes of rotation was less than one-third for an actuator having an overall length of 3 V2 inches. and intersect at points 102 and 104. The combined movements of the interconnected components thereby provide for the limited upward and sideward movement of the arm actuator as indicated by the arrows 106 and 108. The positive engagement to actuate the interlock switch means is attained throughout many door member oper-.

ations. The mechanical linkage components are fabricated of materials to provide for longevity in operation and a minimum of interference with gasket energy seals surrounding the access opening. The described structure may be mounted solely at the top portion of the door member 18 or such structure may be disposed at both the top and bottom of a side-hinged door assembly. The structure is also adaptable to other access door arrangements wherein the door movement controls the engagement of safety interlock switch means. To further provide for the positive engagement of the spring lever arm 80 of the interlock switch 78 by arm actuator 44 it is possible to provide a flat plate 110 of a relatively large dimension at the contacting end of the spring 80.

Numerous other variations, modifications or alterations in both the structure, as well as material composition, will suggest themselves to those skilled in the art. it is intended, therefore, that the foregoing description of the illustrative embodiment of the invention be considered in its broadest aspects and not in a limiting sense.

I claim: 1. Microwave oven apparatus comprising: an enclosure having an access opening; a door member for closing said access opening; a microwave energy source adapted to radiate energy within said enclosure; an electrical circuit for energizing said source and controlling the operation of said apparatus including safety interlock switch means; and nonspring-biassed mechanical linkage means for actuating said interlock switch means operatively associated with said door member including a first pivoted member and a second pivoted member interconnected to said first member with said first and second members having independent axes of rotation about a fixed pivot member; said fixed pivot members being juxtapositioned and spaced apart substantially less than the length of said first pivoted member when said. door member is closed;

said first pivoted member being secured to a peripheral wall of said door member and having a free end to engage and actuate said switch means; said second pivoted member being secured to 21 peripheral wall of said access opening and having structure to constrain and guide the movement of said first member for positive engagement of said switch means when said door member is closed.

2. The apparatus according to claim 1 wherein said first pivoted member comprises a substantially rectangular shaped metallic arm acuator.

3. The apparatus according to claim 1 wherein said second pivoted member comprises a bushing member having a slot to receive and slidably engage said first pivoted member.

4. The apparatus according to claim 3 wherein said bushing member comprises separate upper and lower body members adapted to be interlocked.

5. The apparatus according to claim 3 wherein said bushing member comprises a body member of a substantially rigid plastic material. 

1. Microwave oven apparatus comprising: an enclosure having an access opening; a door member for closing said access opening; a microwave energy source adapted to radiate energy within said enclosure; an electrical circuit for energizing said source and controlling the operation of said apparatus including safety interlock switch means; and nonspring-biassed mechanical linkage means for actuating said interlock switch means operatively associated with said door member including a first pivoted member and a second pivoted member interconnected to said first member with said first and second members having independent axes of rotation about a fixed pivot member; said fixed pivot members being juxtapositioned and spaced apart substantially less than the length of said first pivoted member when said door member is closed; said first pivoted member being secured to a peripheral wall of said door member and having a free end to engage and actuate said switch means; said second pivoted member being secured to a peripheral wall of said access opening and having structure to constrain and guide the movement of said first member for positive engagement of said switch means when said door member is closed.
 2. The apparatus according to claim 1 wherein said first pivoted member comprises a substantially rectangular shaped metallic arm acuator.
 3. The apparatus according to claim 1 wherein said second pivoted member comprises a bushing member having a slot to receive and slidably engage said first pivoted member.
 4. The apparatus according to claim 3 wherein said bushing member comprises separate upper and lower body members adapted to be interlocked.
 5. The apparatus according to claim 3 wherein said bushing member comprises a body member of a substantially rigid plastic material. 